Bass pedal connection problems

I'm having some trouble connecting my bass pedal to my bass trigger.

For starters I have a Roland KD8 (not a KD9) for a bass trigger. When I used my gibraltar avenger2 single pedal it didn't give me any problems.

But now I have a Tama Iron Cobra double bass pedal and I'm having some issues. I can get it on there and tighten it down as far as it will go, but it's setting on top of that "bump." It rocks back and forth violently while I'm playing and then just comes off altogether. What can I do to fix this?

I have the same issue and I have DTXplorers bass drum pad. I dont know what it is but it doesnt really matter to me. That didnt happen to me when I had another pedal. I think that Iron Cobra pedal doesnt fit to the bass drum but can be used.

I had two idea's but I don't think one of em will work so I'm down to one.

"Mill" out a spot on the hook up part so it fits down on the bump.